Unstan (or Onstan, or Onston) is a Neolithic chambered cairn located about 2 mi (3 km) north-east of Stromness on Mainland, Orkney, Scotland.

[5] In Orkney, the tombs became increasingly elaborate; the number of compartments reached a maximum of fourteen at the Knowe of Ramsay on Rousay.

The remaining walls rise to a height of almost 2 m (6.6 ft),[8] and consist primarily of thin stacked slabs of local flagstone[9] that come from the Devonian Old Red Sandstone.

Unstan ware typically consists of elegant shallow bowls with a band of grooved patterning below the rim,[16] created using a technique known as "stab-and-drag".

Most of the bowls were shattered or incomplete; this is common in chambered cairns and suggests that the vessels were intentionally broken for inclusion with the dead.

[7] Human remains were found in Unstan – there were two crouched skeletons in the side cell, several more in the main compartment,[1] and a number of bones were scattered throughout the rest of the tomb.

It is possible that Unstan was in use well into the second millennium BC; an arrowhead was discovered in the tomb that is characteristic of the Beaker People who lived from the Late Neolithic into the Bronze Age.